Abstract
The investigations were carried out to assess surface chemistry, morphology and depth profile of Hg for gas processing pipe steel coupon of API 5L-X52 after adsorption with elemental Hg at 25 0C in the presence of air. The effect of Hg adsorption periods and surface Hg levels were investigated as well as characterization of Hg depth profiles. No reasonable correlation was observed between surface Hg levels and Hg adsorption periods. Forms of Hg found on the top surface and in the depth profile were in oxide and elemental forms, respectively. However, most of Hg present was superficial and did not penetrate below the surface. The lowest concentration of 0.2 Molar of iodine and 2.0 Molar of potassium iodide was significantly found to work well with all ranges of Hg contamination with the final surface Hg levels of less than 0.1 atom% of Hg by the XPS analysis with relative percentage of Hg removal of about 99%.
Highlights
This study assesses mercury levels both on the surface and in the depth profile, and further identifies an optimum iodine concentration for use in the decontamination by the iodine/iodide lixiviant method
We found no reasonable correlation between the surface Hg levels and the adsorption periods for either of the surface analysis techniques used
We observed mercury as spherical droplets of Hg0 attached on the steel coupon surface at the end of each adsorption period, and found the Hg concentration ranged from less than 5 to about 45 atom% by Energy Dispersive X-Ray (EDX) analysis
Summary
This study assesses mercury levels both on the surface and in the depth profile, and further identifies an optimum iodine concentration for use in the decontamination by the iodine/iodide lixiviant method. Reproducing in the laboratory a high pressure environment to match that of the subsea pipeline would be possible, but very difficult. Because of the relatively high incompressibility of liquid mercury, the interaction between mercury and steel is not expected to be a strong function of pressure. The study was performed at ambient pressure. Ambient temperature (25°C) is a reasonable match to the temperatures of the subsea pipeline
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